A deterministic bio-economic model was used to investigate the impact of different heifer replacement breeding systems for beef suckler cow production in different environments. It was shown that measures of cow efficiency were highly correlated with profitability in suckled calf production. However, where significant genotype differences exist in final output value due to issues of carcass quality, then more complete characterization of system profitability is recommended. In systems utilizing a terminal sire mating policy for all matings in excess of replacement heifer requirements the proportion of terminal sire matings made are affected by female fertility. Reduced cow fertility combined with late attainment of puberty in heifers and low heifer fertility has a substantial negative effect on the proportion of terminal sire matings made. This illustrates an aspect of production that can be improved by the use of crossbreeding to exploit heterosis in reproductive traits. The time frame of impacts of the different systems was seen to vary. Grading up to a pure breed allowed exploitation of heterosis in the early years of the transition leading to a boost in profitability but this boost was lost as the herd became purebred. Composite and rotational crossing systems were seen to create a steady rise in financial margin to the point where they became stable in breed proportion and heterosis. The effect of cow size was evaluated in three different environments, representing UK lowland, upland and hill. It was found that small cows became more profitable in relation to large cows as food resources became more limiting. In a non-limiting environment large cows were more profitable than small cows.